OOSMARIUM. 81 



semicells from the base cuneate-seroicircular ; end view ellip- 

 tical with a prominent central elevation; laterally seen, obo- 

 vate-circular with a mamilliform prominence on each side. 



Diameter 28 <>..; length :>Q a. 



Collected this form from ponds on Mount Everett, Mass. 

 It corresponds so nearly with a plant found on the island of 

 Java, described by Dr. Nordstedt, 1 adopt the name of his 

 choice. 



( '. homalodermum, Nord. Plate XVII. figs. 1!'. 20. 



Slightly longer than bmad, deeply constricted ; sinus narrow 

 linear with the mouth considerably ampliated ; semicells 

 trapezoid with a subreniform base; sides refuse; ends trun- 

 cate, and often retuse : superior angles obtuse, inferior broadly 

 rounded ; seen from the vertex, elliptical-oblong with the 

 middle, somewhat inflated ; lateral view ovate. Ends about 

 half a- wide a- the breadth of the cell. Cytioderm finely, 

 often indistinctly, punctate. 

 Diameter 40 //. 



Ponds, Mount Everett, Mass. 



The typical plant was found in the Arctic region, on the 

 island of Spitzbergen. It is described by Dr. Nordstedt as 

 measuring 4<s-f>l it. in diameter, about one-fifth larger than 

 our plant; hitherto found only in one locality, L881 and 1882. 



C. cruciatum, Breb. Plate Will. figs. 23, 24. 



Length and breadth nearly the same, ends broadly truncate ; 

 deeply constricted ; sinus narrow, enlarged outwardly; semi- 

 cells trapezoid-reniform, inferior angles obtuse j sides incline 

 towards the truncate end ; margins somewhat donate. Two 

 nuclei in each semicell ; membrane finely granulate or punctate. 

 Diameter 22-24 a. 



Swamp and marsh pools ; rather rare. 



C. PHASEOLUS, Breb. Plate XVIII, figs. 28 -32. 



Cells about as long as wide, smooth ; constriction deep, 

 forming a linear, excavated, notch on each side; semicells re- 

 niform; end view elliptic with a slight projection in the 

 middle of each side. 



A common species to be found, probably, in every State of 

 the Union. 

 6 



